1. Field of the Invention
Titania (TiO.sub.2) is excellent in properties such as ultraviolet absorbability, adsorbability and the like. Accordingly, it has been widely used as a material in such applications as 1 an ultraviolet absorber, a masking agent in an anti-sunburn agent, a paint, a film and the like; 2 an absorber, an adsorbent, a deodorizer and the like.
Further, nowadays the superior photocatalytic activity of titania is given attention. The titania is applied to environmental cleanup or the like upon decomposition of carbonaceous gas or nitrogen oxides while utilizing the superior properties thereof, such as oxidation or reduction.
The improvement of the properties of titania, especially the photocatalytic activity in the above-mentioned usages has been in demand.
2. Description of Related Art
As one of the conventional technologies for improving the properties of titania, it is known that if titania is doped with SiO.sub.2, the specific surface area can be increased.
In order to improve the photocatalytic activity, the present inventors tried to chemically treat the TiO.sub.2 powder obtained by a sol-gel method, having large specific surface area, with an NaOH aqueous solution to improve the photocatalytic activity, and reported this technology in the following literature.
(1) "Preprints of Symposium of Catalyst Chemistry related to Light", Jun. 6, 1996, held by Rikagaku Kenkyusyo and Catalyst Academy, p. 24-25 PA1 (2) "Preprints of Annual Meeting of The Ceramic Society of Japan 1996", Apr. 2 to 4, 1996, p. 170